The objectives have been to study representative malignancies in vivo and in vitro as to their transplantability, inducibility with chemicals and radiation, type C virus activity and development of host resistance by vaccination. Low cancer incidence mice exposed to x-irradiation came down with lymphomas, some of which yielded transplantable tumor lines and xenotropic type C virus. Some anti-cancer vaccines resulted in increase in the resistance to tumor challenge. More potent specific vaccines are to be tested. Transplantation of human neoplasms to athymic nude mice resulted in propagation of some malignant tumors and rejection of benign inocula.